Traffic Recovery in Openflow Networks

1. A method of supporting traffic recovery at a switching node of an OpenFlow network, wherein the switching node has a plurality of ports and the switching node has at least one flow table for storing flow entries which determine forwarding of received packets between the ports, the method comprising: receiving an instruction from a controller to configure a backup path at the switching node; installing a flow entry for the backup path in the at least one flow table of the switching node; monitoring an idle period for which a flow entry has not been used; and renewing the flow entry for the backup path based on at least one of: an association between the flow entry for the backup path and a flow entry for a working path at the switching node, wherein the flow entry for the backup path is renewed when the flow entry for the working path is used to forward a received packet; receiving a flow entry renewal packet from another switching node on the backup path; wherein the renewing comprises resetting the idle period.

2. A method according to claim 1 wherein the association is between the flow entry for the backup path and the flow entry for the working path, wherein the flow entry for the working path defines a forwarding from a first port and the flow entry for the backup path defines a forwarding from a second port.

3. A method according to claim 1 wherein there is a plurality of flow entries for backup paths and the plurality of flow entries are associated with the flow entry for the working path at the node.

4. A method according to claim 1 further comprising receiving an instruction to configure the working path at the switching node and installing a flow entry for the working path in the at least one flow table of the switching node.

5. A method according to claim 4 wherein the flow entry for the working path has a higher priority entry compared to the flow entry for the backup path.

6. A method according to claim 5 further comprising determining a failure in the working path and, in response to determining the failure, removing the flow entry associated with the working path and using the flow entry for the backup path to forward received packets.

7. A method according to claim 1 further comprising sending a flow entry renewal packet to another switching node of the backup path.

8. A method according to claim 1 further comprising determining a failure of a link connected to one of the ports of the switching node and, in response to determining the failure, removing any of the flow entries in the at least one flow table which use that port.

9. A method according to claim 1 wherein each flow entry comprises a source address and a destination address and the step of renewing the flow entry for the backup path based on an association between the flow entry for the backup path and a flow entry for a working path at the node comprises associating flow entries with the same source address and destination address.

10. A method according to claim 1 wherein the step of renewing the flow entry for the backup path based on receiving a flow entry renewal packet from another switching node comprises receiving a flow entry renewal packet carrying information which matches a flow entry for the backup path.

11. A method according to claim 10 wherein the flow entry for the backup path comprises a source address and a destination address and wherein the flow entry renewal packet includes the same source address and destination address.

12. A method according to claim 10 wherein the flow entry renewal packet comprises a field indicating that the packet is for the purpose of flow entry renewal.

13. A method according to claim 1 further comprising: receiving an instruction from the controller to configure the sending of flow entry renewal packets along the backup path; sending, on a periodic basis, a flow renewal packet to another switching node on the backup path.

14. Apparatus for use at a switching node of an OpenFlow network comprising: a plurality of ports for connecting to links to other switching nodes; at least one flow table for storing flow entries which determine forwarding of received packets between the ports; an interface for communicating with a controller; a flow entry installation module which is arranged to receive an instruction from the controller to configure a backup path at the switching node and to install a flow entry for the backup path in the at least one flow table; and a flow entry renewal module which is arranged to renew the flow entry for the backup path based on at least one of: an association between the flow entry for the backup path and a flow entry for a working path at the node, wherein the flow entry for the backup path is renewed when the flow entry for the working path is used to forward a received packet; receiving a flow entry renewal packet from another switching node on the backup path.

15. Apparatus for use at a controller of an OpenFlow network, the OpenFlow network comprising a plurality of switching nodes, the apparatus comprising: an interface for communicating with the switching nodes, wherein the interface is arranged to receive a request for a protected traffic path between a first switching node and a second switching node of the OpenFlow network; a working path route computation module arranged to compute a working path between the first switching node and the second switching node of the OpenFlow network via at least one intermediate switching node; a backup path route computation module arranged to compute a backup path between the first switching node and the second switching node; a recovery module arranged to send instructions to the switching nodes to configure the working path and the backup path and to send an instruction to configure at least one of the switching nodes on the working path to periodically send a flow renewal packet along the backup path to renew the flow entry for the backup path in switching nodes of the backup path.

16. A method of supporting traffic recovery in an OpenFlow network comprising a controller connected to a plurality of switching nodes, wherein the switching nodes are connected by links, the method comprising, at the controller: receiving a request for a protected traffic path between a first switching node and a second switching node of the OpenFlow network; computing a working path between the first switching node and the second switching node of the OpenFlow network via at least one intermediate switching node; computing a plurality of backup paths between the first switching node and the second switching node; sending instructions to the switching nodes to configure the working path and the plurality of backup paths.

17. A method according to claim 16 wherein each of the plurality of backup paths corresponds to a different possible point of failure in the working path.

18. A method according to claim 17 wherein the step of computing a plurality of backup paths is performed for a point of failure in each link of the working path.

19. Apparatus for use at a controller of an OpenFlow network, the OpenFlow network comprising a plurality of switching nodes, the apparatus comprising: an interface for communicating with the switching nodes, wherein the interface is arranged to receive a request for a protected traffic path between a first switching node and a second switching node of the OpenFlow network; a working path route computation module arranged to compute a working path between the first switching node and the second switching node of the OpenFlow network via at least one intermediate switching node; a backup path route computation module arranged to compute a plurality of backup paths between the first switching node and the second switching node; a recovery module arranged to send instructions to the switching nodes to configure the working path and the plurality of backup paths.